The present invention generally relates to a storage device.
The method generally used to control a magnetic disk device involves turning the power ON when access is received, executing rotation of the magnetic storage medium, responding to access by a host computer, and, after access is complete, turning OFF the power of the motor used to rotate the magnetic storage medium in a stepwise fashion. That is, magnetic disk devices contain various power saving modes and mainly possess a function to select a predetermined power saving mode when access is being received and to automatically shift to this mode.
A storage device comprises a storage unit in which a plurality of magnetic disk devices are connected in the form of an array and provides a host computer such as a server with logical storage areas (‘LU’ hereinbelow) comprising a plurality of magnetic disk devices. In order to increase reliability and so forth, the storage device provides the host computer with RAID (Redundant Array of Independent Disks)-based redundant LU. In such a storage device, in cases where there is very little access by the host computer, there is no need for all the magnetic disk devices to be operating. However, when a magnetic disk device temporarily stops rotating, same is unable to immediately respond to access by the host computer. Usage of the above control method that is generally employed for magnetic disk devices means that it takes time for the magnetic disk devices to operate in the event of an access request and the overall performance of the storage device drops considerably.
Therefore, in the case of the technology that appears in Japanese Application Laid Open No. 2000-293314, a technology which manages the positions of the magnetic disk devices that constitute the LU as well as the state of the access by the host computer to the logical volumes and which, in cases where there is no access to a logical volume in a magnetic disk device for a predetermined time (referred to as ‘period A’ hereinbelow), selects one of a plurality of power saving modes and shifts the magnetic disk device to the selected power saving mode has been disclosed (See Japanese Application Laid Open No. 2000-293314).
According to the technology that appears in Japanese Application Laid Open No. 2000-293314, in cases where the storage device provides an application for which access occurs intermittently with an LU, for example, a need sometimes arises to set period A which is the period in which it is judged that there is no access by the application to several hours depending on the access cycle of the application.
However, even in the case of such an application for which access occurs intermittently, the operation is sometimes such that access to the storage device does not occur for a long period as is the case during a scheduled stoppage at night. In the case of such an operation, a magnetic disk device is desirably shifted to a variety of power saving modes at the moment when the scheduled stoppage takes place in order to reduce power consumption.
However, with the technology that appears in Japanese Application Laid Open No. 2000-293314, unless a number of hours have elapsed since the storage device is accessed, the processing to shift the magnetic disk device to a variety of power saving modes is not executed. That is, excess power is consumed by a magnetic disk device which is known to have not been accessed by an application for several hours.